Suspension

ABSTRACT

A suspension of an annular secondary structure on a primary structure, in the form of a spoke-type centering device, has at least three sliding guides distributed uniformly over the structure circumference. Each sliding guide allows at least a linear relative movement of the structures transversely to their axial direction. The linear direction of movement of each sliding guide runs, in relation to the structure-related radial direction at the location of the sliding guide, at an angle having radial and tangential direction components.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to the suspension of an annular secondarystructure on a primary structure, in particular of a stator structureacted upon by hot gas on a casing structure of a gas turbine, in theform of what may be referred to as a spoke-type centering device.

Spoke-type centering devices are used in order to suspend annularsecondary structures centrically on mostly likewise annular or tubularprimary structures. In this case, radial relative movements of thestructures in relation to one another are to be possible essentiallywithout constraining forces and deformations, while at the same timeconcentricity is maintained. The principle is appropriate, inparticular, when widely differing thermal expansions of two concentricstructures are to be compensated. If the secondary structure isrelatively elastic, that is to say has low dimensional stability, itshould be, as far as possible, stabilized and stiffened via thesuspension.

German patent publication DE 198 07 247 C2 discloses a turbomachine withrotor and stator, which has at least one specially designed guide-vanering. The latter is designed as a self-supporting component with areinforcement on the inner shroud and with a segmented outer shroud. Theguide-vane ring is positioned in the casing of the turbomachine via aspoke-type centering device having at least three “spokes”. The slidingguides of the spoke-type centering device have bearing journals inbearing bushes, and the linear direction of movement in each slidingguide runs radially with respect to the guide-vane ring and casing.

It is likewise customary to implement the sliding guides by way ofsliding blocks running in straight grooves, the direction of movementrunning, as is usual, radially with respect to the coupled structures.Experience shows that pronounced wear often occurs on the slidingelements of conventional spoke-type centering devices. Permanentdeformations of the thin-walled secondary structures have sometimes beendetected. Both types of damage indicate that higher forces than shouldoccur under ideally rotationally symmetrical conditions obviously arisein the guides. The cause is probably non-rotationally symmetricalexpansion states of the structures, which, in gas turbines, may bebrought about, in particular, by non-homogeneous gas temperaturedistributions. Especially where structures of large diameter areconcerned, with a multiplicity of sliding guides, that is to say of“spokes”, the risk of the occurrence of high constraining forcesincreases. By virtue of geometry, the orientation of the direction ofmovement changes only slightly from guide to guide, so that, in theevent of expansion of the secondary-structure region located betweenthem, jamming may occur in both guides because of a fall below the angleof friction, with the result that free structure expansion becomesimpossible. A further disadvantage of the conventional radial spoke-typecentering devices is that these “soft” secondary structures arestiffened only when there is an odd number of sliding guides (“spokes”).

In view of these disadvantages of known spoke-type centering devices,one object of this invention is to find a suspension for an annularsecondary structure on a primary structure in the manner of a spoke-typecentering device having at least three differently oriented slidingguides. The suspension prevents or largely reduces the constrainingforces and deformations, and also wear, and makes it possible to stiffenflexible secondary structures, irrespective of whether there is an evenor odd number of sliding guides.

According to the invention, the linear direction of movement of eachsliding guide is inclined at an angle β to the radial direction of thestructures, so that the relative movement acquires a radial componentand a tangential component. Guide jamming, with all its disadvantages,is thereby avoided with a high degree of reliability. This applies tohomogeneous and non-homogeneous dimensional changes of the secondarystructure. In the case of homogeneous rotationally symmetrical expansionor contraction of the secondary structure, the latter also executes asmall relative rotation in relation to the primary structure forkinematic reasons, which in most cases is acceptable. In the case ofnon-homogeneous locally differing expansion or contraction of thesecondary structure, the latter is deformed elastically to some extentaway from the annular configuration. However, the sliding-guide forcesresulting from this are substantially lower than during the jamming of aconventional radial spoke-type centering device. The dimensionaldeviations are likewise kept within acceptable limits. One effect of theinvention, namely to increase dimensional stability, may permit thesecondary structure to be designed to be more elastic and lighter thanin a conventional spoke-type centering device.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in more detail below with reference to thefigures.

FIG. 1 shows a cross section through a suspension with eight slidingguides, reproducing two different rotationally symmetrical expansionstates of a secondary structure,

FIG. 2 shows a part cross section through the suspension according toFIG. 1 with an asymmetric expansion state of the secondary structure,

FIG. 3 shows a sliding guide with a rigid sliding block and slot,

FIG. 4 shows a sliding guide with a pivotable sliding block and a slot,and

FIG. 5 shows a sliding guide with a pin and a bush.

DETAILED DESCRIPTION OF THE INVENTION

The illustrations according to FIGS. 1 and 2 are as far as possible indiagrammatic form, in order to reproduce the invention as simply andclearly as possible. The suspension 1, in the form of what may bereferred to as a spoke-type centering device, comprises eight slidingguides 10 which are distributed uniformly on the circumference. Theangular interval of the guides thus amounts to 45°. The structures,primary structure 2 and secondary structure 6, which are coupled bymeans of the suspension 1, are indicated in actual fact only as hatchedfragments in the upper region of FIG. 1. Instead of the real annularsecondary structure 6, a closed polygon with rigid chords S1 to S8 andwith joints between the chords in the sliding guides 10 is consideredhere. The eight radial straight lines emanating from the structurecenter and in each case offset at 45° indicate only thestructure-related radial direction R to the or in the chord joints andare not to be understood as structural elements. The sliding guide 10 onthe angle bisecting line (45°) of the right upper quadrant shows thatthe linear direction of movement L of the sliding guide 10 deviates byan angle β from the radial direction R and therefore, de facto, has aradial and a tangential movement component. The selected angle β ispreferably larger than the maximum angle of friction α to be expected inthe sliding guide 10, so that, with a high degree of reliability, thereneed be no fear of jamming of the sliding-guide pairing. In the presentconceptually simplified suspension 1 which has an articulated chordpolygon and the sliding guides 10 of which are inclined clockwise at anangle β to the radial direction R, the change in length (expansion,contraction) of a chord leads to a sliding movement in the sliding guideat the chord end located clockwise at the front, since, on each chord,in each case only one sliding guide is inclined to the transversedirection of the chord by markedly more than the angle of friction,whereas the other sliding guide is approximately transverse to thechord.

To understand these kinematics more clearly, the sliding guide 10 at thetop right in FIG. 1 is given additional particulars. In addition to thestructure-related radial direction R at the location of the slidingguide, to the linear direction of movement L of the sliding guide 10 andto the angle β between R and L, there can also be seen, represented bydashes and dots, the straight prolongation V of the chord S8, thetransverse direction T, at an angle of 90° to the chord S8, and theangle βeff between L and T. Furthermore, dots indicate what may bereferred to as the friction cone of the sliding guide 10, the apex angleof which is twice as large as the angle of friction α. Since, here, thedirection of movement L runs perpendicularly to the adjacent chord S7,the friction cone is mirror-symmetrical with respect to S7. Since theprolongation V lies well outside the friction cone, a change in lengthof S8 leads to a defined jam-free movement of the “joint” between S8 andS7 in the L-direction. It would therefore be sufficient, in theory, forthe selected angle βeff to be larger than α. Since a real homogeneoussecondary structure behaves differently from the simple articulatedchord polygon, for safety reasons even the angle β should be larger thanα.

For clearer understanding, terms, such as coefficient of friction andangle of friction, will be dealt with briefly at this juncture. Therelation between the coefficient of friction f and the angle of frictionα is as follows:

f=tan α

Hence, α is the inverse function of the tangent of f:

α=inv tan f

The following values for f may be gathered from technicalencyclopaedias:

Solid-state friction f

Metal/metal 0.3÷1.5

Ceramic/ceramic 0.2÷1.5

Plastic/metal 0.2÷1.5

Boundary friction 0.1÷0.2

Mixed friction 0.01÷0.1

Fluid friction ≈0.01

At predetermined actual coefficients of friction, the following anglesof friction are obtained:

f α 0.2 11.3° 0.3 16.7° 0.5 26.6° 1.0 45.0°

As regards the suspension 1 illustrated, with 8 “spokes”, the angle β,amounts to 22.5°. This inclination would probably be sufficient for amaximum coefficient of friction f<0.4. In the case of higher friction,the inclination β to the radial would have to be increasedcorrespondingly.

FIG. 1 illustrates the chords S1 to S8, twice in each case to beprecise, as unbroken and as broken straight lines. The unbroken chordpolygon stands for a “cold” contracted state of the secondary structure6. The broken larger chord polygon stands for a “hot” uniformly expandedstate of the secondary structure 6. The primary structure 2 is in thiscase to remain unchanged geometrically for the sake of simplicity, sothat that part of the sliding guides 10 which belongs to the primarystructure does not move. In the event of an identical expansion orcontraction of all the chords, the angles of articulation of the chordpolygon obviously remain unchanged. This means, in terms of the realsecondary structure 6, that its diameter changes, but not its shape(annulus). The concentric position in relation to the primary structure2 also remains. It can also be seen that, at a transition from theunbroken position to the broken position, the chord polygon, andconsequently the secondary structure, executes a small rotationalmovement clockwise through an angle γ, specifically as a result of theangle β of the sliding guides 10. In practical applications, this slightrotation due to the invention is, as a rule, of no importance for thefunctioning of the structure.

In contrast to FIG. 1, FIG. 2 shows an asymmetric expansion of the chordpolygon. When turbomachines are used in practice, operating states witha highly asymmetric temperature distribution over the flow cross sectionmay occur. Thus, according to FIG. 2, essentially only the chord S1 isto undergo thermal expansion. In this case, the sliding guide 10 at the“joint” between S1 and S8 executes a yielding movement obliquely upwardsand to the right at the angle β. The chord S8 is in this case co-pivotedabout its right-hand “joint” in relation to the chord S7, but inpractice does not change its length. As a consequence of the kinematicspredetermined by the sliding guides 10, a movement in the sliding guide10 between S1 and S8 upwards and to the right, with the chord length ofS8 remaining the same, results in only a negligible movement in thesliding guide between S8 and S7 downwards to the left, which practicallycannot be illustrated in FIG. 2. Thus, de facto, the chord S8 executesonly a pivoting movement about its “joint” in relation to S7, and thechord S7 remains in its position, as does the chord S2. It can be seen,however, that the “angles of articulation” between the chords S2/S1,S1/S8 and S8/S7 change. This means, in terms of the real secondarystructure 6, that it is deformed asymmetrically and is no longer exactlycircular. In this case, however, the actual changes in dimension and inshape are, as a rule, so small that their effects on functioning and onmechanical load can be ignored. The constraining forces and deformationsoccurring without the present invention would, as a rule, be moreharmful.

FIGS. 3 to 5 show actual exemplary embodiments of sliding guides 11 to13 with an inclination β according to the invention.

FIG. 3 shows a sliding guide 11 with a sliding block 14 in a slot 17.The slot 17 is integrated into the primary structure 3, and the slidingblock 14 is connected firmly to the secondary structure 7 or is workedout from the latter. The sliding block 14 is deliberately illustratedwith rounded corners and with sliding-surface clearance in the slot 17.During operation, for example in the event of asymmetric structuredeformation, slight tilting movements to the sliding block 14 in theslot 17 may occur, clearance and corner rounding being intended toprevent excessive friction, wear and jamming.

FIG. 4 likewise shows a sliding guide 12 with a slot 18 integrated intothe primary structure 4 and with a sliding block 15, although, incontrast to FIG. 3, the latter is pivotable about a shaft 16 which isconnected firmly to the secondary structure 8. Small relative rotationsof the structures 4, 8 are thereby easily possible. The fit of thesliding block 15 in the slot 18 can be made precise and largely free ofplay.

Finally, FIG. 5 shows a sliding guide 13 with a pin 19 in a bush 21. Thepin 19, here, is connected firmly to the primary structure 5, and thecircular-cylindrical bush 21 is integrated into a thickening of thesecondary structure 9. The outer surface 20 of the pin 19 has a convexand rotationally symmetrical shape, in order to avoid edge stress orjamming during structure rotation. The convex shape may correspond, inan extreme case, to a spherical shape.

What is claimed is:
 1. A suspension of an annular secondary structure ona primary structure, the suspension being of a stator structure actedupon by hot gas on a casing structure of a gas turbine, in the form of aspoke-type centring device comprising at least three sliding guideswhich are distributed over a structure circumference at equal angularintervals, each of the guides allowing at least a linear relativemovement between the primary and the secondary structures transverselyto their axial direction, a linear direction of movement changing fromone sliding guide to the next by an angle which corresponds to anangular interval of the sliding guides, wherein the linear direction ofmovement of each sliding guide in relation to a structure-related radialdirection at the location of the sliding guide runs at an angle having aradial direction component and a tangential direction component.
 2. Thesuspension according to claim 1, wherein the angle is defined as afunction of a maximum angle of friction to be expected in each slidingguide.
 3. The suspension according to claim 2, wherein each slidingguide comprises a sliding block and a slot or a pin and a bush, whereineach sliding block or pin is connected to one of the structures, andwherein each slot or bush is connected to the other of the structures.4. The suspension according to claim 3, wherein at least one of thesliding block and the slot, sliding on each other, has a wear-resistantmetallic and/or ceramic sliding-surface coating.
 5. The suspensionaccording to claim 3, wherein at least one of the pin and the bush,sliding on each other, has a wear-resistant metallic and/or ceramicsliding-surface coating.
 6. The suspension according to claim 3, whereinthe sliding block of each sliding guide has convexly curved slidingsurfaces, or wherein the pin of each sliding guide has a convex outersurface.
 7. The suspension according to claim 6, wherein at least one ofthe sliding block and the slot, sliding on each other, has awear-resistant metallic and/or ceramic sliding-surface coating.
 8. Thesuspension according to claim 6, wherein at least one of the pin and thebush, sliding on each other, has a wear-resistant metallic and/orceramic sliding-surface coating.
 9. The suspension according to claim 3,wherein the sliding block of each sliding guide is arranged pivotablyabout a shaft oriented in the axial direction of the primary andsecondary structures.
 10. The suspension according to claim 9, whereinat least one of the sliding block and the slot, sliding on each other,has a wear-resistant metallic and/or ceramic sliding-surface coating.11. The suspension according to claim 9, wherein at least one of the pinand the bush, sliding on each other, has a wear-resistant metallicand/or ceramic sliding-surface coating.
 12. The suspension according toclaim 1, wherein each sliding guide comprises a sliding block and a slotor a pin and a bush, wherein each sliding block or pin is connected toone of the structures, and wherein each slot or bush is connected to theother of the structures.
 13. The suspension according to claim 3,wherein at least one of the sliding block and the slot, sliding on eachother, has a wear-resistant metallic and/or ceramic sliding-surfacecoating.
 14. The suspension according to claim 12, wherein at least oneof the pin and the bush, sliding on each other, has a wear-resistantmetallic and/or ceramic sliding-surface coating.
 15. The suspensionaccording to claim 12, wherein the sliding block of each sliding guidehas convexly curved sliding surfaces, or wherein the pin of each slidingguide has a convex outer surface.
 16. The suspension according to claim15, wherein at least one of the sliding block and the slot, sliding oneach other, has a wear-resistant metallic and/or ceramic sliding-surfacecoating.
 17. The suspension according to claim 15, wherein at least oneof the pin and the bush, sliding on each other, has a wear-resistantmetallic and/or ceramic sliding-surface coating.
 18. The suspensionaccording to claim 12, wherein the sliding block of each sliding guideis arranged pivotably about a shaft oriented in the axial direction ofthe primary and secondary structures.
 19. The suspension according toclaim 18, wherein at least one of the sliding block and the slot,sliding on each other, has a wear-resistant metallic and/or ceramicsliding-surface coating.
 20. The suspension according to claim 18,wherein at least one of the pin and the bush, sliding on each other, hasa wear-resistant metallic and/or ceramic sliding-surface coating.